Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using a cardioplegia solution.
The development of minimally invasive techniques for cardiac bypass grafting, for example, by Heartport, Inc., Redwood City, Calif. and CardioThoracic Systems, Inc., Menlo Park, Calif. have placed a premium on reducing the size of equipment employed in the sterile field. Whereas open surgical techniques typically provide a relatively large surgical site that the surgeon views directly, minimally invasive techniques require the placement of endoscopes, video monitors, and various positioning systems for the instruments. These devices crowd the sterile field and can limit the surgeon's ability to maneuver.
At the same time, however, the need to reduce priming volume of the oxygenator and pump, and the desire to reduce blood contact with non-native surfaces has increased interest in locating the oxygenator and pump as near as possible to the patient.
In recognition of the foregoing issues, some previously known cardiopulmonary systems have attempted to miniaturize and integrate certain components of cardiopulmonary systems. U.S. Pat. Nos. 5,266,265 and 5,270,005, both to Raible, describe an extracorporeal blood oxygenation system having an integrated blood reservoir, an oxygenator formed from a static array of hollow fibers, a heat exchanger, a pump and a pump motor that is controlled by cable connected to a control console.
One drawback of systems of the type described in foregoing patents, however, arises during priming of the extracorporeal circuit, and in particular, in the need to use large quantities of saline or donor blood to prime the systems. Such fluids are required to flush air out of the system and, because they are relatively incompressible, ensure that the pump used in the extracorporeal circuit develops sufficient pressure head to propel oxygenated blood back to the patient.
In view of this limitation of previously known blood handling systems, it would be desirable to provide a blood handling system and methods that automatically remove air from an extracorporeal blood circuit.
It further would be desirable to blood handling systems and methods that permit one or more additional blood processing components, such as a heat exchanger, to be added to an extracorporeal blood circuit without having to prime the component prior to bringing that component online, thereby reducing disruption to operation of the blood handling system.
It also would be desirable to provide an extracorporeal blood handling system and methods wherein the blood handling system has compact size and low surface area, and reduces contact between the blood and foreign surfaces, thus reducing priming volume, hemolysis and platelet activation.
It still further would be desirable to provide a blood handling system and methods that provide progressive filtration of blood passing through the system, thus reducing the risk that a single blood filter element will become clogged during extended operation.